Method and material for isolating a severe loss zone

ABSTRACT

A method and drilling fluid additive for reducing severe fluid losses in a well, comprising a combination of granular scrap tire particles and polymer adhesive molded into a capsule shape. Once in the severe loss zone, a plurality of LCMs wedge into the formation fractures and seal off the severe loss zone.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/631,122 filed Feb. 15, 2018, U.S. Provisional Application Ser.No. 62/631,062 filed Feb. 15, 2018, U.S. Provisional Application Ser.No. 62/631,073 filed Feb. 15, 2018, and U.S. Provisional ApplicationSer. No. 62/631,126 filed Feb. 15, 2018.

TECHNICAL FIELD

The present disclosure relates generally to the use of a loss controlmaterial (or lost circulation material, in either event, LCM) as a wayto seal fractures that form in a drilled wellbore. More specifically, itrelates to the use of a plurality of engineered LCMs with at least oneof a conical shape, a capsule shape, a spherical shape, an ovoid shape,or combinations of these, and elastically deformable construction. Thisengineered LCM forms a seal within severe loss zone fractures, therebyreducing or eliminating the amount of drilling fluid lost during awellbore drilling operation.

BACKGROUND

Drilling fluid loss—commonly referred to as lost circulation—is asignificant problem in the oil and gas industry. Lost circulation arisesfrom wellbore drilling that penetrates into geological formations thatare fractured, cavernous, vugular, underpressured, or highly permeable,such as those with a permeability greater than 100 Darcys. Lostcirculation is typically classified into four volumetric loss ratecategories or zones, depending on the amount of fluid lost per unit oftime: seepage losses are those associated with the loss of less thanabout 10 barrels per hour; partial losses are those associated with theloss of between about 10 barrels per hour and about 100 barrels perhour; severe losses are those associated with the loss of over about 100barrels per hour; while total losses are those where no fluid returns tothe surface of the wellbore and that typically necessitates abandoningthe well. Typically, the sizes of these geological voids can becorrelated to whether the potential for drilling fluid loss fits intoone of these four categories.

Lost circulation can be prevented in some circumstances through the useof pre-drilling geomechanical models and related analytical tools, aswell as through the use of reinforced wellbore wall and relatedstrengthening. In circumstances where such preventive measures do notprovide ample protection against lost circulation, LCMs may beintroduced as an LCM pill or via the drilling fluid as a remediationapproach. While exhibiting some benefit, these LCMs have traditionallybeen ineffective for severe loss zones such as those that arise fromfractures with openings that exhibit conical, ovular, elliptical,circular, semi-circular, pseudo-cylindrical, triangular, curvi-planar orother shapes, as well as the various sizes of these fractures.

SUMMARY

Lost circulation encountered while drilling is a major problem in theoil and gas industry that is difficult to combat in severe loss zones.The LCMs typically introduced into the wellbore to combat severe lossesare cheap, easy to access materials. These small LCMs may be easilydislodged from the wellbore fractures and allow further fluid lossinstead of packing the fractures and effectively preventing fluid loss.However, these materials are typically individual rubber particles thatare not adhered to each other, or, if there is an adhesive, the rubberparticles adhered to each other do not form a shape capable of beingcompressed and wedged into fractures. These conventional materials arenot engineered for the specific purpose of remediating severe losses,and therefore are not effective at blocking the severe zone.Accordingly, an improved approach to reducing or eliminating the loss ofdrilling fluid for such severe loss zones is warranted. The LCMs asdescribed in this disclosure include rubber particles and a polymeradhesive that binds the rubber particles together to form a shape, suchas a cone, capsule, sphere, or ovoid. These LCMs are resilient and arecapable of being compressed and wedged into fractures, blocking thesevere loss zone and remediating severe losses.

According to one embodiment, a method of reducing lost circulation in asevere loss zone of a wellbore is disclosed. The method includespreparing a drilling fluid by combining a liquid carrier with aweighting material and an additive and introducing the drilling fluidinto the severe loss zone such that numerous cone-shaped LCMs becomelodged in at least one fracture that defines the severe loss zone. Theadditive includes numerous cone-shaped LCMs. This material is composedof numerous granular scrap tire particles and a polymer adhesive that isdispersed between the granular scrap tire particles and binds thegranular scrap tire particles together introducing a drilling fluidcomprising a liquid carrier, a weighting material and a plurality ofadditives into the severe loss zone such that the plurality of additivesbecome lodged in at least one fracture that defines the severe losszone, the plurality of additives comprising: cone-shaped LCMs,capsule-shaped LCMs, spherical-shaped LCMs, ovoid-shaped LCMs, or acombination of these, and the LCMs comprise: a plurality of granularscrap tire particles; and a polymer adhesive that is dispersed betweenthe plurality of granular scrap tire particles and binds the pluralityof granular scrap tire particles together.

According to a second embodiment, an LCM additive for a drilling fluidis disclosed. The additive includes cone-shaped LCMs, capsule-shapedLCMs, spherical-shaped LCMs, ovoid-shaped LCMs, or a combination ofthese. The LCMs include a plurality of granular scrap tire particles anda polymer adhesive that is dispersed between the granular scrap tireparticles and binds the granular scrap tire particles together.

According to yet another embodiment, a drilling fluid is disclosed. Thedrilling fluid includes a slurry including a liquid carrier, a weightingagent, and an LCM additive. The LCM additive includes cone-shaped LCMs,capsule-shaped LCMs, spherical-shaped LCMs, ovoid-shaped LCMs, or acombination of these. The LCM includes a plurality of granular scraptire particles and a polymer adhesive that is dispersed between thegranular scrap tire particles and binds the granular scrap tireparticles together.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of specific embodiments of thepresent disclosure can be best understood when read in conjunction withthe following drawings, where like structure is indicated with likereference numerals and in which:

FIG. 1 depicts three cone-shaped LCMs of varying dimensions, in whichthe cone-shaped LCMs comprise granular scrap tire particles mixed with apolymer adhesive;

FIG. 2 illustrates a drilling assembly as referenced in this applicationfor delivering the cone-shaped LCMs to the severe loss zones;

FIG. 3 illustrates a wellbore drilled in a fractured formation and thecone-shaped LCMs that penetrated the fractures and sealed the zone.

FIG. 4 depicts three different sizes of capsule-shaped LCMs inaccordance with one or more embodiments shown or described;

FIG. 5 illustrates a wellbore drilled in a fractured formation and thecapsule-shaped LCMs that penetrated the fractures and sealed the zone;

FIG. 6 depicts three different sizes of spherical-shaped LCMs inaccordance with one or more embodiments shown or described;

FIG. 7 illustrates a wellbore drilled in a fractured formation and thespherical-shaped LCMs that penetrated the fractures and sealed the zone;

FIG. 8 depicts three ovoid-shaped LCMs of varying dimensions, in whichthe ovoid-shaped LCMs comprise granular scrap tire particles mixed witha polymer adhesive; and

FIG. 9 illustrates a wellbore drilled in a fractured formation and theovoid-shaped LCMs that penetrated the fractures and sealed the zone.

DETAILED DESCRIPTION

The LCMs of this disclosure are directed to holistically address thevarious shapes of fractures in loss zones. Loss zones may includecone-shaped fractures, capsule-shaped fractures, sphere-shapedfractures, ovoid-shaped fractures, or combinations of these. Loss zonesdominated by cone-shaped fracture openings of various base diameters andcone lengths can be effectively sealed and blocked by a resilientelastic rubber sealant material shaped into cones of variabledimensions. The apex of the cone-shaped LCM will guide the cone into thefractures to create a wedging effect in the opening of the fracture dueto the squeezing pressure applied during the placement of the LCMs andthus can provide an effective solution to lost circulation whiledrilling. As used throughout this disclosure, the term “apex” refers tothe top of the LCM cone. The diameter of the apex may range from 500microns to half the diameter of the base. Due to the wedging effect,these cone-shaped LCMs are an appropriate material to control lostcirculation zones dominated by fractures with conical configurations.The LCM need not have a separate outer coating or material. As usedthroughout this disclosure, the term “lost circulation zone” refers to aformation encountered during drilling into which circulating fluids canbe lost due to fractures in the formation. As used throughout thisdisclosure, the term “formation” refers to a subterranean geologicregion containing hydrocarbons, such as crude oil, hydrocarbon gases, orboth, which may be extracted from the subterranean geologic region.

Loss zones dominated by capsule-shaped fractures (also referred to asfracture openings) of various sizes can be effectively sealed andblocked by comparably-shaped resilient elastic rubber sealantcapsule-shaped LCMs of varying dimensions. In one form, thecapsule-shaped LCMs are configured for use in a wellbore loss zone thatcontains a cylindrical morphology along at least a portion of a lengthof one or more fractures. In one particular form, these wellbore losszones dominated by such fracture (or fracture openings) correspond tosevere loss zones such that the introduction of these capsule-shapedLCMs can reduce or eliminate lost circulation owing at least in part tothe size and generally non-axisymmetric shape of such capsule-shapedLCMs. As used throughout this disclosure, severe loss zones may be foundin fractured, cavernous, vugular, underpressured or highly permeablegeological formations, such as those with a permeability greater than100 Darcys. Severe loss zones generally do not include impermeable orzones with a permeability of less than 10 Darcys, overpressured zones ordeep sand.

The reduction or elimination of lost circulation takes place through theformation of set seals or plugs that result from the capsule-shaped LCMsbecoming lodged into the fractures such that the capsule-shaped LCMsexperience in-situ stresses from the subterranean walls that define thefractures. As such, the resilient nature of the rubber particles, forexample, scrap tire particles, forms an LCM that is malleable, ductile,deforms without failure, and shrinks under pressure to enter fractures.Furthermore, because these capsule-shaped LCMs can be fabricated byusing elastically resilient particles that can be reclaimed from scraprubber (such as discarded automobile tires, which are numerous),environmental benefits may be enjoyed through the reduction in theamount of landfill associated with the discarded tires.

In one form, hemispherical end caps of the capsule-shaped LCM will alloweasy entry of the capsule-shaped LCMs into the fractured flow channelsunder the action of initial flow of fluid into the fractured loss zone,while the larger cylindrical portion will inhibit excessive movement ofthe capsule-shaped LCMs into the fractures, particularly when thecapsule-shaped LCMs encounter narrow footholds, ridges, bulges or narrowbends formed in the flow channels that are defined by the fractures.This in turn leads to choking and associated clogging which in turnmitigates the passage of drilling fluid through these fracture channels.

Loss zones dominated by spherical-shaped LCMs of various sizes can beeffectively sealed and blocked by comparably-shaped resilient elasticrubber sealant spherical-shaped LCMs of varying dimensions. In one form,the spherical-shaped LCMs are configured for use in a wellbore loss zonethat contains spherical morphology along at least a portion of a lengthof one or more fractures.

Loss zones dominated by ovoid-shaped fracture openings of various majoraxis lengths can be effectively sealed and blocked by a resilientelastic rubber sealant material shaped into ovoids of variabledimensions. As used throughout this disclosure, the term “ovoid” refersto an egg-shaped object with a narrow tip and a broad base. The narrowtip of the ovoid-shaped LCM will guide the ovoid into the fractures tocreate a wedging effect in the opening of the fracture due to thesqueezing pressure applied during the placement of the LCMs and thus canprovide an effective solution to lost circulation while drilling. Asused throughout this disclosure, the term “narrow tip” refers to thenarrower end of the LCM ovoid. The diameter of the narrow tip may rangefrom 500 microns to half the length of the minor axis length. Due to thewedging effect, these ovoid-shaped LCMs are an appropriate material tocontrol lost circulation zones dominated by fractures with ovoidconfigurations. The LCM need not have a separate outer coating ormaterial.

As referenced previously, lost circulation is typically classified intofour volumetric loss rate categories. Typically, the size of thesegeological voids can be correlated to whether the potential for drillingfluid loss fits into one of these four zones. As used throughout thisdisclosure, the term “drilling fluid” refers to any of a number ofliquid and gaseous fluids and mixtures of fluids and solids (as solidsuspensions, mixtures and emulsions of liquids, gases and solids) usedin operations to drill boreholes into the earth. These geological voids,or fractures, may be measured by running logs down the annulus todetermine the opening size of the fractures. As used throughout thisdisclosure, the term “annulus” refers to the space between twoconcentric objects, such as between the wellbore and casing or betweencasing and tubing, where fluid can flow. Likewise, the term “pipe” mayrefer to drill collars, drill pipe, casing or tubing.

Referring first to FIG. 1, an LCM additive for a wellbore drilling fluidis shown. In one form, the cone-shaped LCMs 100 comprise a plurality ofgranular scrap tire particles 120 and a polymer adhesive 130 that isdispersed between the plurality of granular scrap tire particles 120 andbinds the plurality of granular scrap tire particles 120 together. Asused throughout this disclosure, the term “granular scrap tireparticles” refers to rubber particles manufactured from removing atleast one of dust, steel fibers, and textile fibers prior to breakingdown a tire into individual rubber particles with a particle sizeranging from 500 microns to 10,000 microns each. The resultingcone-shaped LCMs 100 form a resilient elastic rubber sealant materialthat is malleable, ductile, deforms without failure, and shrinks underpressure to enter fractures. The granular scrap tire particles 120 mixwith the polymer adhesive 130 such that the polymer adhesive 130 isdispersed between the granular scrap tire particles 120, binding thegranular scrap tire particles 120 together and holding the granularscrap tire particles 120 in place throughout the cone-shaped LCMs 100.In one embodiment, the plurality of granular scrap tire particles 120comprises at least one of styrene-butadiene rubber (SBR) and ethylenepropylene diene monomer (EPDM) rubber.

More specifically, this polymer adhesive 130 may comprise, but is notlimited to, a polyurethane-based material. As used throughout thisdisclosure, the term “polyurethane” refers to a synthetic resin polymeradhesive composed of organic units joined by urethane links.Alternatively, the polymer adhesive 130 may comprise, but is not limitedto, a reaction product of an aromatic polyisocyanate-prepolymer based ondiphenylmethane diisocyanate.

In another embodiment, the LCM additive comprises up to 30% polymeradhesive 130 by volume (vol. %), from 10 to 40 vol. % polymer adhesive130, or from 20 to 30 vol. % polymer adhesive 130.

The polymer adhesive 130 may not be substituted with a substance such aswax, because wax would lose cohesion with the granular scrap tireparticles 120 in the high pressure and temperature conditions of thelost circulation zone. Wax begins to melt into a liquid at about 99° F.and would not bind the granular scrap tire particles 120 together at atemperature greater than 99° F.

FIG. 1 shows three different sizes of the cone-shaped LCMs 100, whereone cone-shaped LCM 100A comprises a base diameter 170 of 7.5centimeters (cm), a slant length 140 of 10 cm, and a surface area of atleast 117 cm². In a second embodiment, the cone-shaped LCM 100Bcomprises a base diameter 180 of 5 cm, a slant length 150 of 7.5 cm, anda surface area of at least 58 cm². In a third embodiment, thecone-shaped LCM 100C comprises a base diameter 190 of 2.5 cm, a slantlength 160 of 5 cm, and a surface area of at least 19 cm². In anotherembodiment, the cone-shaped LCMs 100 may comprise a base diameterranging from 2.5 to 7.5 centimeters, a slant length ranging from 5 to 10centimeters, and a conical surface area of at least 19 squarecentimeters. The cone-shaped LCMs may be formed in a variety of sizes infurther embodiments, not limited to the sizes described in thisdisclosure.

Referring next to FIG. 2, a drilling assembly 200 used for reducing lostcirculation in a severe loss zone 310 of a wellbore is shown. As usedthroughout this disclosure, the term “severe loss zone” refers to a lostcirculation zone in which the amount of fluids lost per hour falls intothe severe losses category. Severe loss zones may be found in fractured,cavernous, vugular, underpressured, or highly permeable formations, suchas those with a permeability greater than 100 Darcys. As used throughoutthis disclosure, the term “underpressured” refers to a formation with apore pressure that is less than hydrostatic pressure. However, severeloss zones 310 do not include impermeable or low permeability zones,overpressured zones, or deep sand. It will be appreciated that althoughthe drilling assembly 200 is illustrated for the recovery or extractionof such hydrocarbons, the disclosed materials, equipment and associatedtechniques may be useful in circulating fluids in a wellbore for otherpurposes, such as for drilling or related operations, as well as thosewellbore 216 operations where variable-density drilling fluid 222 may beused, such as for deeper wellbores 216 that can help maintain adequatelevels of hydrostatic pressure as a way to avoid an influx of formationfluid (gas or liquid).

The method may comprise introducing a drilling fluid 222 and a pluralityof LCM additives 100 into the severe loss zone 310 such that theplurality of cone-shaped LCMs 100 becomes lodged in at least onefracture 300 that defines the severe loss zone 310. Although theplurality of LCM additives is depicted as a plurality of cone-shapedLCMs, it is to be understood that the plurality of LCM additives may beany of cone-shaped LCMs, capsule-shaped LCMs, spherical-shaped LCMs,ovoid-shaped LCMs, or a combination of these. The drilling fluid 222 isformed by combining a liquid carrier with a weighting material. As usedthroughout this disclosure, the term “weighting material” can refer tobarite, calcium carbonate, hematite, siderite, ilmenite, or combinationsof these. These weighting materials will increase the density orviscosity of the drilling fluid 222, thereby making the drilling fluid222 more capable of carrying large solids, such as the LCM additives100, downhole.

Referring next to FIG. 3, the drilling fluid 222 may be introduced intothe severe loss zone 310 such that the cone-shaped LCMs 100 becomelodged in the fractures 300 that define the severe loss zone 310; suchlodging forms flow blockage that helps to isolate the severe loss zone310 of the wellbore 226. More specifically, the cone-shaped LCMs 100 maybe used for a severe loss zone 310 comprised of cone-shaped fractureopenings 300. To isolate the severe loss zone 310, the cone-shaped LCMis introduced into the severe loss zone 310 as squeezing pressure isapplied down the wellbore 216. This squeezing pressure causes the apexof the cone-shaped LCM to slide into the cone-shaped fracture openings300, wedging the cone-shaped LCM into the cone-shaped fracture openings300 and sealing the severe loss zone 310.

In one embodiment, the plurality of cone-shaped LCMs 100 have a basediameter ranging from 2.5 to 7.5 centimeters, a slant length rangingfrom 5 to 10 centimeters, and a conical surface area of at least 19square centimeters, and can create a tight seal in cone-shaped fractureopenings 300 with an opening base diameter or gap size smaller than,equal to, or greater than 2.5 centimeters. In another embodiment, themethod further comprises drilling through a plurality of cone-shapedLCMs 100 sealing the severe loss zone 310 to continue drilling thewellbore 216. In another embodiment, the method further comprisesintroducing the plurality of cone-shaped LCMs 100 to the severe losszone 310 through a drill string disposed within the wellbore 216. Inanother embodiment, the method further comprises introducing adisplacement fluid to displace the plurality of cone-shaped LCMs 100into severe loss zone 310.

Referring to FIG. 4, details associated with various sizes ofcapsule-shaped LCMs that are generally identified as 400 are shown,where more particularly the sizes may correspond to small capsule-shapedLCMs 400A, medium capsule-shaped LCMs 400B and large capsule-shaped LCMs400C. Regardless of the size, the capsule-shaped LCMs 100 have acylindrical body section 410 that is symmetric about a rotationalelongate axis A, as well as a pair of hemispherical end cap sections420. In one form, at least the end cap sections 420 define a generallysmooth outer surface, while in another form, the cylindrical bodysection 410 may form a generally smooth outer surface as well.

In one form, the small capsule-shaped LCMs 400A may have an overalllength of between 2 and 3 centimeters, with an overall diameter of 1.5centimeters. In addition, a cylindrical body section 410 may define alength along its axial dimension of 1.75 centimeters such that the axiallength associated with the two opposed end caps is 0.5 centimeters. Thesmall capsule-shaped LCM 400A also has an aspect ratio of 1.5. Althoughthree different sizes of capsule-shaped LCMs 400A, 400B and 400C aredepicted in the present disclosure, it will be appreciated that othersizes with different lengths, diameters and aspect ratios can beengineered to meet any operational demand, and that all such variantsare within the scope of the present disclosure.

Significantly, the orientation of the fractures within a loss zone isnot important, as the capsule-shaped LCMs 400 will work with bothvertical and horizontal fractures. Due to the resilient characteristicsof rubber particles 120 bounded together by the polymer adhesive 130,coupled with the varying sizes and non-axisymmetric profile of theresulting capsule-shaped LCMs 400, they can shrink under pressure toenter into cylindrical or pseudo-cylindrical fractures with an openingor gap size smaller, equal to or greater than the capsule-shaped LCMdimensions in order to create a tight seal at the bulged narrow zones ofthe fractures.

To form the LCMs, rubber particles (also referred to as “crumb rubber”)120 are dispersed throughout a polymer precursor fluid that, when cured,acts as an adhesive-like binder. The rubber particles 120 may be createdthrough suitable rubber recycling activities, such as the recapping orshredding of discarded automotive tires the latter of which may firstinvolve the removal of other tire components such as steel, reinforcingfibers or the like prior to grinding or related particle-producingoperations. Examples of rubber that can be used in granulated orshredded form include natural or synthetic rubbers, such asstyrene-butadiene rubber (SBR), ethylene propylene diene monomer (EPDM)rubber or their variations. In one form, such rubber may be vulcanizedor otherwise cured.

The polymer adhesive 130 may be polyurethane. Examples ofpolyurethane-based materials that may be used as the binder includelatex or oil modified polyurethane. In one form, the polyurethane thatis used as a binding agent for the particulate rubber is a reactionproduct of an aromatic polyisocyanate-prepolymer moisture-curing binderbased on diphenylmethane diisocyanate, a commercial example of which mayinclude PU Binder 1118 from KDF of Thessaloniki, Greece. PU Binder 1118is a 100% solids, moisture curing polyurethane prepolymer. It is MDIbased and solvent free with an expected curing time of between 4 and 6hours in average atmospheric temperatures. PU Binder 1118 has aviscosity of between 3000 and 5000 mPa·s at 25° C., and has an NCOcontent of between 8% and 9.5%. In one form, the mixture of the rubbergranules and binder is air-cured. Other polyurethanes may be used solong as strength of the bonds is sufficient to form the resulting LCMs.In one particular form, the polyurethane is solvent-free.

Referring next to FIG. 5, a simplified cutaway view of the use ofcapsule-shaped LCMs 400 that are situated within fractures 300 that areformed in a severe loss zone 310 of wellbore 216 is shown. As depicted,the loss zones 310 contain nearly equal dimension fractures 300,although it will be appreciated that certain bulges, ledges andfootholds may be present at some locations within the length of thefractures 300. The drilling fluid 222 may be introduced into the severeloss zone 310 such that the capsule-shaped LCMs 400 become lodged in thefractures 300; such lodging forms flow blockage that helps to isolatethe severe loss zone 310 of the wellbore 216. To isolate the severe losszone 310, the capsule-shaped LCMs 400 are introduced into the severeloss zone 310 as squeezing pressure is applied down the wellbore 216.This squeezing pressure causes the hemispherical ends of thecapsule-shaped LCMs 400 to slide into the openings caused by fractures300, which in turn produces a friction-based wedging of thecapsule-shaped LCMs 400 that in turn seals off the severe loss zone 310from any additional fluid flow.

The external surface area of the capsule-shaped LCMs 400 can adjustunder the pressure with a change in their shape and size while stillmaintaining a close contact with the internal surface of the fractures300 of the loss zones 310. Significantly, after the cessation ofpumping, the resilient character of the capsule-shaped LCMs 400 allowsthem to remain in place in order to maintain the tight fit condition andprevent the loss of the drilling fluid 222. As previously discussed, atleast one of the cylindrical body section 410 and the end caps 420 havea smooth outer surface; such construction promotes reduced frictionbetween the capsule-shaped LCMs 400 and the fracture loss zones 310 atleast during such time as the capsule-shaped LCMs 400 are beingintroduced to the fractures 300 along with the drilling fluid 222 toenhance the ability of the capsule-shaped LCMs 400 to seal and plug thefluid escaping channels at the narrow or restricted zone of the flowpath and thus prevent or reduce the loss of whole mud from the wellbore216 into a neighboring formation.

Referring to FIG. 6, details associated with various sizes ofspherical-shaped LCMs that are generally identified as 600 are shown,where more particularly the sizes may correspond to smallspherical-shaped LCMs 600A, medium spherical-shaped LCMs 600B and largespherical-shaped LCMs 600C. Regardless of the size, the spherical-shapedLCMs 600 have a spherical body section that in one form may possess agenerally smooth outer surface.

In one form, the small spherical-shaped LCMs 600A may have an overalldiameter of about 2 centimeters, while the medium spherical-shaped LCMs600B may have an overall diameter of about 4 centimeters and the largespherical-shaped LCMs 600C may have an overall diameter of about 6centimeters. Although three different sizes of spherical-shaped LCMs600A, 600B and 600C are depicted in the present disclosure, it will beappreciated that other sizes with different diameters can be engineeredto meet any operational demand, and that all such variants are withinthe scope of the present disclosure.

Significantly, the orientation of the fractures within a loss zone isnot important, as the spherical-shaped LCMs 600 will work with bothvertical and horizontal fractures. Due to the resilient characteristicsof rubber particles 120 bounded together by the polymer adhesive 130,coupled with the varying sizes and non-axisymmetric profile of theresulting spherical-shaped LCMs 600, they can easily enter intospherical or pseudo-spherical fractures with an opening or gap sizesmaller, equal to or greater than the spherical-shaped LCM dimensions inorder to create a tight seal at the bulged narrow zones of thefractures. Due to the highly elastic characteristic of the scrap tireparticles, the spherical-shaped LCMs 600 can also shrink significantlyunder the action of pressure in order to enter into smaller fracturesand gaps so long as the amount of shrinkage is sufficient for aparticular fracture size.

Referring next to FIG. 7, a simplified cutaway view of the use ofspherical-shaped LCMs 600 that are situated within fractures 300 thatare formed in a severe loss zone 310 of wellbore 216 is shown. Asdepicted, the loss zones 310 contain nearly equal dimension fractures300, although it will be appreciated that certain bulges, ledges andfootholds may be present at some locations within the length of thefractures 300. The drilling fluid 222 may be introduced into the severeloss zone 310 such that the spherical-shaped LCMs 600 become lodged inthe fractures 300; such lodging forms flow blockage that helps toisolate the severe loss zone 310 of the wellbore 216. To isolate thesevere loss zone 310, the spherical-shaped LCMs 600 are introduced intothe severe loss zone 310 as squeezing pressure is applied down thewellbore 216. This squeezing pressure causes the spherical-shaped LCMs600 to slide into the openings caused by fractures 300, which in turnproduces a friction-based wedging of the spherical-shaped LCM 600 thatin turn seals off the severe loss zone 310 from any additional fluidflow.

The external surface area of the spherical-shaped LCMs 600 can adjustunder the pressure with a change in their shape and size while stillmaintaining a close contact with the internal surface of the fractures300 of the loss zones 310. Significantly, after the cessation ofpumping, the resilient character of the spherical-shaped LCMs 600 allowsthem to remain in place in order to maintain the tight fit condition andprevent the loss of the drilling fluid 222. As previously discussed, inone form, the body of the spherical-shaped LCMs 600 has a smooth outersurface; such construction promotes reduced friction between thespherical-shaped LCMs 600 and the fracture loss zones 310 at leastduring such time as the spherical-shaped LCMs 600 are being introducedto the fractures 300 along with the drilling fluid 222 to enhance theability of the spherical-shaped LCMs 600 to seal and plug the fluidescaping channels at the narrow or restricted zone of the flow path andthus prevent or reduce the loss of whole mud from the wellbore 216 intoa neighboring formation.

Referring to FIG. 8, an LCM additive for a wellbore drilling fluid isshown. The additive includes a plurality of ovoid-shaped LCMs 800 ofvarious sizes, each with a narrow tip 810 and a broad base 820. In oneform, the ovoid-shaped LCMs 800 comprise a plurality of granular scraptire particles 120 and a polymer adhesive 130 that is dispersed betweenthe plurality of granular scrap tire particles 120 and binds theplurality of granular scrap tire particles 120 together. The resultingovoid-shaped LCMs 100 form a resilient elastic rubber sealant materialthat is malleable, ductile, deforms without failure, and shrinks underpressure to enter fractures. The granular scrap tire particles 120 mixwith the polymer adhesive 130 such that the polymer adhesive 130 isdispersed between the granular scrap tire particles 120, binding thegranular scrap tire particles 120 together and holding the granularscrap tire particles 120 in place throughout the ovoid-shaped LCMs 800.

FIG. 8 shows three different sizes of the ovoid-shaped LCMs 800 whereone ovoid-shaped LCM 800A comprises a major axis length 830A of 2.125centimeters (cm), a minor axis length 840A of 1.5 cm, and a surface areaof at least 9 cm². In a second embodiment, the ovoid-shaped LCM 800Bcomprises a major axis length 830B of 4.25 cm, a minor axis length 840Bof 3 cm, and a surface area of at least 36 cm². In a third embodiment,the ovoid-shaped LCM 800C comprises a major axis length 830C of 8.5 cm,a minor axis length 840C of 6 cm, and a surface area of at least 104cm². In another embodiment, the ovoid-shaped LCMs 800 may comprise amajor axis length ranging from 2.125 to 8.5 centimeters, a minor axislength ranging from 1.5 to 6 centimeters, and an ovoid surface area ofat least 9 square centimeters. The ovoid-shaped LCMs 800 may be formedin a variety of sizes in further embodiments, not limited to the sizesdescribed in this disclosure.

Referring next to FIG. 9, the drilling fluid 222 may be introduced intothe severe loss zone 310 such that the ovoid-shaped LCMs 800 becomelodged in the fractures 300 that define the severe loss zone 310; suchlodging forms flow blockage that helps to isolate the severe loss zone310 of the wellbore 226. More specifically, the ovoid-shaped LCMs 800may be used for a severe loss zone 310 comprised of ovoid-shapedfracture openings 300. To isolate the severe loss zone 310, theovoid-shaped LCM 800 is introduced into the severe loss zone 310 assqueezing pressure is applied down the wellbore 216. This squeezingpressure causes the narrow tip 810 of the ovoid-shaped LCM 800 to slideinto the ovoid-shaped fracture openings 300, wedging the ovoid-shapedLCM 800 into the ovoid-shaped fracture openings 300 and sealing thesevere loss zone 310.

In one embodiment, the plurality of ovoid-shaped LCMs 800 have a majoraxis length ranging from 2.5 to 7.5 centimeters, a minor axis lengthranging from 5 to 10 centimeters, and an ovoid surface area of at least19 square centimeters, and can create a tight seal in ovoid-shapedfracture openings 300 with an opening major axis length or gap sizesmaller than, equal to, or greater than 2.5 centimeters. In anotherembodiment, the method further comprises drilling through plurality ofovoid-shaped LCMs 800 sealing the severe loss zone 310 to continuedrilling the wellbore 216. In another embodiment, the method furthercomprises introducing the plurality of ovoid-shaped LCMs 800 to thesevere loss zone 310 through a drill string disposed within the wellbore216. In another embodiment, the method further comprises introducing adisplacement fluid to displace the plurality of ovoid-shaped LCMs 800into severe loss zone 310.

This disclosure also recites a drilling fluid comprising a slurry madeof a weighting material and a liquid carrier, and the LCM additive. Theliquid carrier may comprise an aqueous-based liquid, or, alternatively,an oil-based liquid.

EXAMPLE

The following examples illustrate features of the present disclosure butare not intended to limit the scope of the disclosure.

Example 1

To demonstrate the improved stability, sample cone-shaped LCMs weresubmerged in a water solution and a mineral oil solution for 72 hoursand evaluated every 24 hours.

TABLE 1 Time Water Solution Mineral Oil Solution 24 Hours Nodisintegration No disintegration 48 Hours No disintegration Nodisintegration 72 Hours No disintegration No disintegration

In these tests, the LCMs held their shape, showed dimensional stabilitywhether immersed in water or mineral oil solutions. Specifically, therewas minimal to no degradation, disintegration, or dispersion of thegranular scrap tire particles held together by the polyurethane binderduring the 72 hour testing. Here, this means that the overall dimensionsof the cone-shaped LCMs samples were not reduced by more than 5%; thedimensions of the cone-shaped LCMs samples were essentially the samebefore and after testing.

Example 2

To quantify the resiliency of the LCMs, a LCM sample was placed in ametallic cell and an axial force of 10,000 pounds per square inch (psi)was applied to the LCM sample. The LCM sample included 20 wt. % PUBinder 1118, available from KDF, calculated by weight of the LCM sample.The rubber used in the LCM sample was black SBR rubber granulesavailable from SARPCO. The density of the LCM sample was 0.8 grams percubic centimeter (g/cc). The resiliency was determined using thefollowing equation:

${{Resiliency}\mspace{11mu}(\%)} = {100\left( {\left( \frac{h_{r}}{h_{0}} \right) - 1} \right)}$

The initial length of the LCM sample was measured before the resiliencytesting. The axial force of 10,000 psi was then applied to the sample,and the compressed length of the sample, h₀, and the unconfinedcompressive strength (UCS) of the LCM sample was measured. The samplewas then allowed to expand after the axial force was released and anuncompressed sample length, h_(r), was measured. The results of theresiliency test are shown in Table 1:

TABLE 1 Resiliency Test Results Initial length h_(o) h_(r) DeformationResiliency (mm) (mm) (mm) Percentage (%) Percentage (%) UCS (Psi) 65.7833.15 64.26 49.62 93.88 541.25

As shown in Table 1, the resiliency of the LCM sample was measured to be93.88%. This means that the LCM sample is very resilient and capable ofbeing compressed and wedged into fractures, and then expanding withinthe fracture, thereby sealing the fracture.

A first aspect of the present disclosure may be directed to a method ofreducing lost circulation in a severe loss zone of a wellbore, themethod comprising: introducing a drilling fluid comprising a liquidcarrier, a clay-based material and an additive into the severe loss zonesuch that a plurality of ovoid-shaped LCMs becomes lodged in at leastone fracture that defines the severe loss zone. The additive comprisesthe plurality of ovoid-shaped LCMs. The plurality of ovoid-shaped LCMscomprises a plurality of granular scrap tire particles; and a polymeradhesive that is dispersed between the plurality of granular scrap tireparticles and binds the plurality of granular scrap tire particlestogether.

A second aspect of the present disclosure may include the first aspect,in which the plurality of ovoid-shaped LCMs have a major axis lengthranging from 2.125 to 8.5 centimeters, a minor axis length ranging from1.5 to 6 centimeters, and an ovoid surface area of at least 9 squarecentimeters, and can create a tight seal in an ovoid-shaped fracturewith an opening major axis length or gap size smaller than, equal to, orgreater than 2.125 centimeters.

A third aspect of the present disclosure may include the first andsecond aspects, in which the method further comprises drilling throughthe plurality of ovoid-shaped LCMs sealing the severe loss zone tocontinue drilling the wellbore.

A fourth aspect of the present disclosure may include any of the firstthrough third aspects, in which the method further comprises introducingthe plurality of ovoid-shaped LCMs to the severe loss zone through adrill string disposed within the wellbore.

A fifth aspect of the present disclosure may include any of the firstthrough fourth aspects, in which the method further comprisesintroducing a displacement fluid after the plurality of ovoid-shapedLCMs to displace the plurality of ovoid-shaped LCMs into severe losszone.

A sixth aspect of the present disclosure may be directed to a lostcirculation material additive for a drilling fluid, the additivecomprising a plurality of ovoid-shaped LCMs comprising: a plurality ofgranular scrap tire particles; and a polymer adhesive that is dispersedbetween the plurality of granular scrap tire particles and binds theplurality of granular scrap tire particles together.

A seventh aspect of the present disclosure may include the sixth aspect,in which the polymer adhesive comprises a polyurethane-based material.

An eighth aspect of the present disclosure may include the sixth andseventh aspects, in which the polymer adhesive comprises a reactionproduct of an aromatic polyisocyanate-prepolymer based ondiphenylmethane diisocyanate.

A ninth aspect of the present disclosure may include any of the sixththrough eighth aspects, in which the plurality of granular scrap tireparticles comprises at least one of styrene-butadiene rubber andethylene propylene diene monomer rubber.

A tenth aspect of the present disclosure may include any of the sixththrough ninth aspects, in which the plurality of granular scrap tireparticles defines a maximum linear dimension of between 500 microns to10,000 microns each.

An eleventh aspect of the present disclosure may include any of thesixth through tenth aspects, in which the lost circulation materialadditive comprises 20% to 30% polymer adhesive.

A twelfth aspect of the present disclosure may include any of the sixththrough eleventh aspects, in which a single LCM of the plurality ofovoid-shaped LCMs has a major axis length ranging from 2.125 to 8.5centimeters, a minor axis length ranging from 1.5 to 6 centimeters, andan ovoid surface area of at least 9 square centimeters.

A thirteenth aspect of the present disclosure may be directed to adrilling fluid comprising: a slurry comprising a liquid carrier; and alost circulation material additive comprising a plurality ofovoid-shaped LCMs comprising: a plurality of granular scrap tireparticles; and a polymer adhesive that is dispersed between theplurality of granular scrap tire particles and binds the plurality ofgranular scrap tire particles together.

A fourteenth aspect of the present disclosure may include the thirteenthaspect, in which the slurry further comprises a clay-based material.

A fifteenth aspect of the present disclosure may include the thirteenthand fourteenth aspects, in which the liquid carrier comprises awater-based liquid.

A sixteenth aspect of the present disclosure may include any of thethirteenth through fifteenth aspects, in which the liquid carriercomprises a petroleum-based liquid.

A seventeenth aspect of the present disclosure may include any of thethirteenth through sixteenth aspects, in which a single LCM of theplurality of ovoid-shaped LCMs has a major axis length ranging from2.125 to 8.5 centimeters, a minor axis length ranging from 1.5 to 6centimeters, and an ovoid surface area of at least 9 square centimeters.

Having described the subject matter of the present disclosure in detailand by reference to specific embodiments of these, it is noted that thevarious details disclosed in this disclosure should not be taken toimply that these details relate to elements that are essentialcomponents of the various embodiments described in this disclosure, evenin cases where a particular element is illustrated in each of thedrawings that accompany the present description. Further, it will beapparent that modifications and variations are possible withoutdeparting from the scope of the present disclosure, including, but notlimited to, embodiments defined in the appended claims.

It is noted that one or more of the following claims utilize the term“in which” as a transitional phrase. For the purposes of defining thepresent invention, it is noted that this term is introduced in theclaims as an open-ended transitional phrase that is used to introduce arecitation of a series of characteristics of the structure and should beinterpreted in like manner as the more commonly used open-ended preambleterm “comprising.”

What is claimed is:
 1. A plurality of lost circulation materialadditives for a drilling fluid, the additives comprising: ovoid-shapedLost Circulation Materials (LCMs) comprising: a plurality of granularscrap tire particles; and a polymer adhesive that is dispersed betweenthe plurality of granular scrap tire particles and binds the pluralityof granular scrap tire particles together, such that the LCMs arecompressed and wedged into fractures with openings in a subsurface losszone, in which the openings are ovoid-shaped, and in which theovoid-shaped LCMs and the openings have: a major axis length rangingfrom 2.125 to 8.5 centimeters, and a minor axis length ranging from 1.5to 6 centimeters.
 2. The additives of claim 1, in which the polymeradhesive comprises a reaction product of an aromaticpolyisocyanate-prepolymer based on diphenylmethane diisocyanate.
 3. Theadditives of claim 1, in which the plurality of granular scrap tireparticles comprises at least one of styrene-butadiene rubber andethylene propylene diene monomer rubber.
 4. The additives of claim 1, inwhich each of the additives comprises from 20 to 30 vol. % of thepolymer adhesive.
 5. The additives of claim 1, in which the polymeradhesive comprises a polyurethane-based material.
 6. The additives ofclaim 1, in which the plurality of granular scrap tire particles definesa maximum linear dimension of between 500 microns to 10,000 micronseach.
 7. The additives of claim 1, in which: the polymer adhesivecomprises a reaction product of an aromatic polyisocyanate-prepolymerbased on diphenylmethane diisocyanate; the plurality of granular scraptire particles comprises at least one of styrene-butadiene rubber andethylene propylene diene monomer rubber; and each of the additivescomprises from 20 to 30 vol. % of the polymer adhesive.
 8. A fluidcomprising: a slurry comprising a liquid carrier; a weighting agent; anda plurality of lost circulation material additives, the additivescomprising ovoid-shaped Lost Circulation Materials (LCMs) comprising: aplurality of granular scrap tire particles; and a polymer adhesive thatis dispersed between the plurality of granular scrap tire particles andbinds the plurality of granular scrap tire particles together, such thatthe LCMs are compressed and wedged into fractures with openings in asubsurface loss zone, in which the openings are ovoid-shaped, and inwhich the ovoid-shaped LCMs and the openings have: a major axis lengthranging from 2.125 to 8.5 centimeters, and a minor axis length rangingfrom 1.5 to 6 centimeters.
 9. The fluid of claim 8, in which: thepolymer adhesive comprises a reaction product of an aromaticpolyisocyanate-prepolymer based on diphenylmethane diisocyanate; theplurality of granular scrap tire particles comprises at least one ofstyrene-butadiene rubber and ethylene propylene diene monomer rubber;and each of the additives comprises from 20 to 30 vol. % of the polymeradhesive.
 10. The fluid of claim 8, in which the polymer adhesivecomprises a polyurethane-based material.
 11. The fluid of claim 8, inwhich the polymer adhesive comprises a reaction product of an aromaticpolyisocyanate-prepolymer based on diphenylmethane diisocyanate.
 12. Thefluid of claim 8, in which the plurality of granular scrap tireparticles comprises at least one of styrene-butadiene rubber andethylene propylene diene monomer rubber.
 13. The fluid of claim 8, inwhich the plurality of granular scrap tire particles defines a maximumlinear dimension of between 500 microns to 10,000 microns each.